This invention relates to cooling device for vapor-cooling semiconductor devices and particularly power semiconductor rectifiers.
Vapor cooling systems utilizing the phase transition of the cooling medium and having an electrically insulating property and condensability at and adjacent room temperature are suitable for cooling high capacity semiconductor elements each capable of generating heat in an amount exceeding, for example, 1 kilowatt. This is because a very small temperature differential provides a thermal flux of high density. Under these circumstances, the heat generated by the semiconductor elements is required to be transported and dissipated to the exterior with a high efficiency because the semiconductor elements are small in size but handle large amounts of electric power. The best use of the characteristic features of the vapor cooling systems of the type referred to is made in connection with semiconductor elements for handling large amounts of power and more particularly with the planar types thereof. In general, planar semiconductor elements are arranged in a stack of alternate heat dissipation plates or blocks and semiconductor elements by means of a compressible contacting mechanism. Since this measure permits the resulting assembly to be small sized and economical, devices including the stack as above described are the object of the present invention.
If a stack having a plurality of planar semiconductor elements alternating in compressive contact relationship with heat dissipation blocks is horizontally disposed then the main heat dissipation surfaces of the blocks or elements lie in the vertical planes. This is important in view of the boiling and cooling operations for the following reasons: where there is a large amount of heat handled, the cooling operation can be continuously performed by upwardly moving bubbles of the particular cooling medium immediately after their formation on the heat dissipation surfaces and then contacting the liquid phase of the cooling medium.
The process as above described can be used with semiconductor elements of types other than the planar type because the resulting structure may include heat dissipation surfaces having vertical portions thereof with a suitable area to serve as the heat dissipation surfaces of the semiconductor elements and mounting plates therefor.
One or more of the stacks thus formed can be transversely disposed in accordance with the size of the resulting device thereby to immediately drive bubbles of a cooling medium generated on the heat dissipation portions into those portions located thereabove. In this case a plurality of stacks may be required to be put upon one another. In order to make the cooling effect uniform, it is desirable to limit the number of rows into which the stacks are disposed and vertically dispose the stacks at suitable intervals while each of the stacks is laterally displaced from the adjacent stack thereby to prevent the upward movement of the cooling medium from being impeded.
The vapor phase of the cooling medium should be condensed into the liquid phase through heat exchange between the same and the exterior, for example, the air after which the liquid phase thus formed again contributes to the cooling of the device.
It is important and also an object of the present invention that the cooling medium is caused to repeatedly pass through the boiling and condensing cycles with a high efficiency in order to provide large capacity devices.
Early systems for vapor cooling semiconductor devices have been based upon the concept that the vapor phase generated from the liquid cooling medium should be used to the condensing surface as rapidly as possible for more effective cooling. Thus vapor cooling devices have comprised the stack or stacks as above described immersed in an amount of a cooling medium charged into the lower portion of the vessel and the condenser means disposed in the upper portion of the same vessel or located above the vessel and in fluid communication with the latter. Such conventional cooling devices have encountered a common problem in that the flow of cooling medium in its vapor phase can not be certainly controlled so that temperature differentials occur on various portions of the condensing means with the result that it is difficult to operate the condensing means at its maximum efficiency.